a. Field of Invention
The present invention relates to means and method for desorbing water from soil samples, and in particular, relates to an improved structure and method for performing such procedures, either with a single soil sample, or with multiple soil samples.
b. Problems in the Art
The uses and advantages of soil water desorption are well known within the art. Such procedures allow hydraulic characteristics of soil samples to be derived and studied.
This type of analysis is valuable in agriculture, agronomy, and environmental applications, to name but a few. A specific example is the study of how agricultural machinery traffic over the soil can affect its ability to transport and store water, which in turn impacts on crop production.
The process of water desorption is defined as removing sorbed substances by the reverse of adsorption or absorption. In order to test soil characteristics such as the porosity of the soil (which in turn can determine how it can handle and store water), one procedure which is utilized to desorb water, is to take the soil sample (which has at least some sorbed water in it), and place it in a container which can be pressurized (called pressure cells). The container has some means (generally one end or wall) which serves as a filter in the sense it allows only passage of water when the container is raised to a certain air pressure. The amount of air pressure needed to force the corresponding amount of water from the soil sample is then utilized to understand the energy state at which that amount of water was held by the soil sample. This in turn can be converted into an understanding of the structure or hydraulic characteristics of the soil.
Described another way, soil generally is a complex composition of soil particles and pores or channels. This allows soil to adsorb and absorb water, as well as transport water through the soil in response to certain pressures.
By widely known physical properties, water adheres to pores and channels in the soil. This "adhesion force" must be overcome by some other force or energy to remove the water from the pores or channels. Therefore, procedures have been used applying known quantities of air pressure to soil samples and correlating the amount of water removed from the pressure cell to the adhesion force for that water in the soil. Then predictions and estimations are made of what the structure of the soil sample is to create that amount of adhesion force.
Some presently conventional structures utilized for soil water desorption are Buchner funnels, Tempe cells, and tension tables. These are well known to those of ordinary skill in the art. While these methods and structures are widely used, it has been found that each has limitations and deficiencies. A real need in the art exists for advancement and improvement in the means and methods used for soil water desorption.
For example, Buchner funnels and Tempe cells are costly and somewhat fragile. They also generally utilize ceramic or fritted glass plates as filters and therefore are subject to plugging. These sorts of concerns illustrate the room for improvement which exists with these devices concerning economy, reliability, and efficiency.
Tension tables are relatively inexpensive but also have deficiencies. First of all, they utilize only lower pressure potentials. Also, their structure requires constant vigilance and frequent maintenance to prevent entry of air into the system.
As is known in the art, pressure cells require that a portion or wall of the cell be sealed off by filter material that under super-atmospheric pressure of sufficient value allows the water to be forced through the pores in the material. In conventional pressure cell systems such material has been, for example, ceramic plate, fritted glass, glass beads, sand, and silt.
Significant problems exist with maintaining a sufficient difference in air pressure between the inside of the pressure cell and the outer side of the filter to allow sufficient pressure differentials to move all the water or at least most of the water out of the soil sample and cell. Obviously, such materials as glass beads, sand, and silt are relatively loose porous materials, whereas ceramic plate and fritted glass are tight, rigid, and can have very small pores. As can be appreciated, the former three substances allow fairly easy passage of water at minimum pressure differentials, but would not allow high pressure differentials to be maintained. No satisfactory material has been found for economical and flexible use with soil desorption.
One known attempt has been made to utilize a considerably different material for the filter. E. L. McCoy, in "Wettable Porous Plastic For Use As A Porous Barrier In Soil Hydraulic Studies", Soil Sci. Soc. Am.J. 53:979-981 (1989) discusses utilizing two porous plastic sheets within a Tempe cell. The advantages found with this material were high water conductance rates (on the order of 0.2 per hour). A significant problem, however, is that the unit is very costly.
It is therefore a principal object of the invention to provide a means and method for soil water desorption which solves or overcomes the problems and deficiencies in the art.
A further object of the present invention is to provide a means and method as above described which allows pressure cells to be pressurized over a wide and sufficient range for various soil water desorption processes.
Another object of the present invention is to provide a means and method as above described which has a structure which is easily disassemblable to allow insertion of soil samples and filters, and yet can be reliably sealed to deter air leaks while in use.
A still further object of the present invention is to provide a means and method as above described which is extremely economical with respect to its parts and to its manufacture.
Another object of the present invention is to provide a means and method as above described which is flexible in how it can be made as far as size, configuration, and positioning.
Another object of the present invention is to provide a means and method as above described which provides low impedance to fluid flow and therefore high flow rates through the filter.
A still further object of the present invention is to provide a means and method as above described which can be used with one pressure cell or with multiple pressure cells or sets of pressure cells.
Another object of the present invention is to provide a means and method as above described which is easily adaptable to a number of different implementations and uses for soil desorption processes and procedures.
Another object of the present invention is to provide a means and method as above described which is efficient, reliable, durable, and economical.
These and other objects, features, and advantages of the present invention will become more apparent with reference to the accompanying specification and claims.